Specialist Estate Agents

Although most people use one of the main property websites when searching if you are after something in particular it pays to look around and see what other estate agents there are.
As well as perhaps doing a search for "property detail + estate agent" you could also search for estate agents in a particular area. Even if they're on rightmove it's worth contacting local agents as they might have useful info on the area and be the first to know of properties coming on to the market.